Cell for pumping a multiphase effluent and pump comprising at least one of the cells

ABSTRACT

A cell for pumping a multiphase effluent includes two rotary parts ( 4-5 ), the first one ( 4 ) having a hydraulic wheel designed for transmitting kinetic energy to each of the multiphase effluent phases entering cell ( 1   a   -1   b ), and the second one ( 5 ), following the first, being an energy converting device designed for homogenizing the phases, transferring kinetic energy between the phases, entraining the lightest phase, converting kinetic energy into pressure and compressing the homogeneous effluent before it leaves the cell. All of the rotary parts of the cell are mounted on a common shaft ( 3 ) axially arranged inside a fixed housing ( 2 ) having an inlet and an outlet for the multiphase effluent.

FIELD OF THE INVENTION

The present invention relates to a cell for pumping a multiphaseeffluent and to a pump comprising such a cell or several of such cellsmounted in series. A multiphase effluent is understood to be an effluentconsisting of a mixture of at least two phases selected from (a) aliquid phase consisting at least of one liquid, (b) a gas phaseconsisting at least of a free gas, and (c) a solid phase consisting ofparticles of at least one solid suspended in (a) and/or (b).

BACKGROUND OF THE INVENTION

Multiphase pumping is a technology used in many industrial sectors, suchas petroleum and gas production (pumping of a petroleum two-phaseeffluent consisting of a mixture of oil and of gas), the chemicalindustries, the nuclear industry (pumping of a mixture of water and ofsteam), and spacecrafts.

The base architecture of industrial pumps used for multiphase effluentpumping includes an impeller (or hydraulic wheel) followed by a stator(or static diffuser). The function of the impeller is to transmitkinetic energy to the mixture to be pumped, the static diffuser thenperforming transfer of the mixture under pressure, in particular to theimpeller of the cell located immediately downstream in the case of apump comprising several pumping cells.

Theoretical studies and tests have shown that there is a relationbetween the liquid single-phase pumping head (H_(L)) and the multiphaseeffluent pumping head (H_(Ph)):

 H _(Ph) =E×H _(L)

where E is the multiphase efficiency, which is essentially a function ofthe void fraction α and of the pressure at the inlet,${{\text{(}\alpha} = \frac{Q_{G}}{Q_{G} + Q_{L}}},$

Q_(G) and Q_(L) being the pumping speeds of the gas G and of the liquidL respectively).

Application of conventional pumps (centrifugal, axial-flow orsemiaxial-flow pumps) to pumping of a mixture of water and steam hasbeen studied in the nuclear field for one-stage pumps (impeller andstator) in order to be able to face up to an exceptional accident in areactor. The tests that have been carried out on that occasion show thatthe two-phase pumping efficiency E greatly decreases as soon as the voidfraction a exceeds 0.15-0.20 and, consequently, the multiphase pumpinghead (H_(Ph)) loses 80% of its liquid single-phase value( H_(L)), whichleads to a multiphase efficiency E=0.2. The main cause is due to theseparation of the phases: the liquid particles are centrifuged in theimpeller, forming a thin liquid film on the external wall. This liquidfilm moves along the external wall of the impeller and of the stator,which leads to a fall in the kinetic energy of the multiphase effluentand to a degradation of the multiphase pumping head (H_(Ph)).

On the basis of this experiment, the petroleum and gas industry hasstudied a helical-axial flow impeller wherein the centrifugation effectis limited and, consequently, part of the liquid phase is kept dispersedin the gas, thus leading to a higher multiphase efficiency E=0.5 to 0.8,for an inlet pressure above 10 bars. For low gas ratios, combination ofa helical-axial flow staged pump followed by a centrifugal pump has beenproposed for pumping at the bottom of oil wells, in FR-A-2,748,533.

However, this result is relative because of the fact that the liquidpumping head (H_(L)) of the helical-axial flow impeller is low inrelation to that of semiaxial-flow pumps, so that, globally, themultiphase pumping head (H_(Ph)) obtained by the two systems iscomparable.

Furthermore, at low pressures (2-3 bars), the multiphase efficiency (E)of existing industrial impellers (semiaxial-flow pumps as well ashelical-axial flow pumps) becomes very low (E being then about 0.1),which is disadvantageous for practical use.

SUMMARY OF THE INVENTION

The aim of the present invention is to propose a pump comprising atleast one multiphase pumping cell capable of providing an interestingliquid pumping head (H_(L)), (which is currently the case forsemiaxial-flow pumps, but not for helical-axial flow pumps) while havinga good multiphase efficiency (E) (which is currently the case forhelical-axial flow pumps, but not for semiaxial-flow pumps).

The present inventor therefore has discovered that, contrary to the ideawhich naturally occurs, according to which the phases should not beseparated, and which is applied in the case of helical-axial flow pumps,at least partial separation of the phases in the impeller could beaccepted and that one could take advantage of the transmission of thehigh kinetic energy of the liquid film to the effluent to be pumped,provided that dynamic means, and not static means, ensuring themechanisms of homogenization of the phases and of their energy levels,then of pressure recovery and finally gas compression are provided. Mostof these means are not implemented in the existing systems once theyhave transmitted the kinetic energy to the (more or less separated)phases, because the stators used in existing pumps are not suited tofulfil these functions. In particular, these conventional stators do notensure the process of energy exchange between the phases and are limitedto transfer of the flows to the outlet in the configuration of more orless separated phases, which leads to a great degradation of themultiphase efficiency (E).

The object of the present invention is thus first a cell for pumping amultiphase effluent, characterized in that it comprises two rotaryparts, the first part consisting of a hydraulic wheel designed fortransmitting kinetic energy to each phase of the multiphase effluententering the cell, and the second part, following the first, consistingof an energy converting device designed for homogenizing the phases,transferring kinetic energy between the phases, entraining the lightestphase, converting kinetic energy into pressure and compressing thehomogeneous effluent before it leaves said cell, all of said rotaryparts being mounted on a common shaft axially arranged inside a fixedhousing comprising an inlet and an outlet for the multiphase effluent.

The two components of the pumping cell according to the presentinvention are thus rotary, unlike existing industrial systems, thesecond component fulfilling, in a new and original way, in combination,several rebalancing functions in relation to the effects due to apartial separation of the phases, also allowed, in a new and originalway, by the first component.

The hydraulic wheel forming the first rotary part of a pumping cellaccording to the present invention generally consists of a boss mountedon the axial shaft and carrying blades exhibiting a hydrodynamic profileto allow transmission of kinetic energy to the multiphase effluent, theblades forming, between the housing and the boss, channels whose lengthis sufficiently great to provide the kinetic energy level required forcarrying the multiphase effluent.

The energy converting device forming the second rotary part of a pumpingcell according to the invention consists, according to a particularlyinteresting embodiment, of at least one continuous or discontinuoushelical wheel carried by a boss mounted on the axial shaft and whichrotates in an energy homogenization and transfer chamber delimited bythe housing and having a section orthonormal to the axis substantiallylarger than the sum of the sections orthonormal to the axis of thechannels of the hydraulic wheel, the extended length of said helicalwheel or of said helical wheels being sufficiantly great for the kineticenergy homogenization and transfer efficiency required for pressurerecovery.

The energy converting device must first homogenize the phases. In thecase of a gas-liquid mixture, this means that the liquid particles mustentrain the gas, transmitting kinetic energy thereto. Mixing musttherefore be long enough, a function that is fulfilled by the helicalwheel(s), a dynamic mixer, capable of homogenizing the phases. Once themixture homogenized, conversion of kinetic energy into pressure isobtained by means of a significant speed decrease due to the increase inthe section of the chamber. Finally, the chamber-helical wheel(s) systemis such that it simultaneously provides compression of the homogeneouseffluent, mainly of its gas phase, before it leaves the cell, and thiseffect can be intensified if the angle of the helical wheel(s) is variedby increasing it in the direction of the cell outlet.

All these functions essential for energy recovery of the pressure in themultiphase effluent are specific to the present invention. Theconventional stator of existing industrial systems does not provide theexchange process between the phases and it is limited to transfer of theflows to the outlet in the configuration of more or less separatedphases, which leads to a degradation of multiphase efficiency E.

After thus describing the preferred main characteristics of the tworotary parts forming the pumping cell according to the invention,non-limitative particular embodiments of the geometry of these two partsare described hereafter:

The ratio of the section orthonormal to the axis of the energyhomogenization and transfer chamber of the energy converting device tothe sum of the sections orthonormal to the axis of the channels of thehydraulic wheel is notably 3 to 10.

The or each continuous or discontinuous helical wheel of the energyconverting device extends over an angle of at least 270° andadvantageously makes a complete turn.

Two or three continuous or discontinuous helical wheels can also beprovided for the energy converting device; they are then advantageouslyand evenly axially shifted and exhibit an angular displacement inrelation to one another of 180° and 120° respectively.

The angle of inclination of a or of each helical wheel of the energyconverting device in relation to a plane perpendicular to the shaft inthe direction of the pumping cell outlet is advantageously of the orderof 10°, and it can increase at the outlet where it can be 20°.

The hydraulic wheel can have a constant or variable diameter, the ratioof the outside diameter (Ds) of said wheel at the outlet to its outsidediameter at the inlet (De) being notably 1 to 3. Unlike well-knownhelical-axial flow impellers, the outside diameter of the hydraulicwheel of the pumping cell according to the present invention canincrease in the direction of the outlet in order to intensify thekinetic energy transfer to the phases.

Furthermore, in relation to well-known semiaxial-flow impellers, it canbe noted that the length of the channels of the hydraulic wheel of thecell according to the present invention is sufficient for energyphenomena to be stabilized, which means that partial separation of thephases is accepted. Under such conditions, in the case of a gas-liquideffluent, the liquid particles whose kinetic energy is highlyconcentrate in the vicinity of the external wall and, at the outlet ofthe hydraulic wheel, inside a channel, there is gas, followed by agas-liquid mixture and by a liquid layer outside.

The channels are advantageously identical, their number can for examplerange between 4 and 10. Their length is notably,${k \times \frac{{De} + {Ds}}{2}},$

k ranging between 0.5 and 1.5.

A static or dynamic flow diffuser device is preferably provided toensure good distribution and continuity of the flow at the outlet of thehydraulic wheel of a pumping cell over the total section of the energyhomogenization and transfer chamber of the associated energy convertingdevice; such a device can advantageously consist of a grate withhydrodynamic profiles carried by the housing and mounted in saidchamber, between the inside of the housing and the helical wheel(s).

The present invention also relates to a pump comprising a multiphasepumping cell as defined above, or several of these cells mounted inseries, the shaft carrying the rotary parts being common to all thecells. The number of these pumping cells is selected to provide themultiphase pumping head required for the application considered.

It can also be noted that the pump according to the invention canreadily fit already existing mechanical pumping structures, the rotaryparts, respectively the specific impeller and the rotary energyconverting device, of a or of each cell according to the inventionrespectively replacing the impeller and the static diffuser of anexisting cell, the existing structure of the housing elements, of theshaft and of the bearings being maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better illustrate the object of the present invention, twoparticular embodiments are described hereafter by way of non limitativeexample, with reference to the accompanying drawings.

In these drawings, FIGS. 1 and 2 are diagrammatic views, partly axialsectional view and partly front view, of two pumping cells, mounted inseries, of a pump respectively in accordance with a first and with asecond embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 shows the two identical pumping cells 1 a and 1 b, mounted inseries, of a pump 1 according to the invention.

Cells 1 a and 1 b are delimited by a housing 2 of general cylindricalshape, along whose axis is arranged a rotating shaft 3 driven by amotor. In the example shown, the multiphase effluent to be pumped firstenters cell 1 a and it flows out through cell 1 b. The extensions ofhousing 2 for delimiting the inflow of the multiphase effluent in pump 1and its outflow are not shown, neither are the bearings supportingrotating shaft 3.

The part of housing 2 associated with a cell consists of two elements ofgeneral annular shape, of equal outside diameter, superposed indiametral planes: an element 2 a, at the cell inlet, with atruncated-cone-shaped inner wall opening out towards the inside, and anelement 2 b, at the cell outlet, having a concave wall directly joiningup with the neighbouring elements 2 a. Part 2 b of the housing comprisesa flow diffuser device consisting of an assembly of hydrodynamicprofiles 12 fastened to the inside of the housing.

Inside each cell 1 a and 1 b, from the inlet to the outlet thereof,shaft 3 successively carries a hydraulic wheel 4 and an energyconverting device 5.

The hydraulic wheel 4 of a cell is arranged in the space delimited bythe associated housing element 2 a and it rotates with a very slightplay in said space. It consists of a boss 6, secured in rotation toshaft 3 and carrying six blades 7 evenly distributed on the peripherythereof. Boss 6 has a truncated-cone-shaped outer wall that opens outtowards the inside of the associated cell, with substantially the sameinclination as the truncated-cone-shaped inner wall of element 2 a inrelation to housing 2, and it comprises end walls at the inlet and atthe outlet of said element 2 a. In the example shown, each blade 7extends, in projection in a diametral plane, over more than 60°, and itis inclined at an angle ranging between 15 (at the inlet) and 35° (atthe outlet) in the direction of the outlet in relation to the mid-planeof boss 6. The Ds/De ratio of hydraulic wheel 4 (Ds and De as definedabove) is here 1.4.

Six peripheral channels 8 allowing inflow of the multiphase effluent ina cell are thus defined, channels whose length is such that a highkinetic energy can be communicated to said effluent by said wheel 4.

Energy converting device 5 consists of a boss 9 of smaller diameter thanboss 6 of wheel 4, which is secured in rotation to shaft 3 and carries ahelical wheel 10 inclined in the direction of the outlet at an angle ofthe order of 10° in relation to the diametral plane and extending overan angle of the order of 270°. Boss 9 is connected to boss 6 ofhydraulic wheel 4 of the next cell (or ends, in the case of outlet cell1 b) by a cupped part 9 a. Rotating helical wheel 10 thus rotates in achamber 11 delimited by part 2 b of housing 2, provided withhydrodynamic diffusers 12, and boss 9-9 a, and converts kinetic energyas defined above up to the cell outlet. Chamber 11 thus has a sectionthat is orthonormal to shaft 3 which, from the inlet, increases inrelation to the outlet section of wheel 4, then decreases in thevicinity of the outlet to form, with part 9 a of boss 9, an annularoutlet directly supplying the inlet of channels 8 in the case of cell 1a. Helical wheel 10 is designed for rotating with a play in a volumecorresponding to that of chamber 11. Considering the energy homogenizingfunction of the helical wheel, it is not necessary for this play to beas limited as that of blades 7.

In this example, the ratio of the section of chamber 11 orthonormal tothe inlet thereof to the sum of the sections of channels 8 is of theorder of 6.

Preliminary tests carried out with the pump of FIG. 1 confirmed thesignificant improvement in the multiphase performances, including at lowpressure at the inlet. FIG. 2 shows a pump 101 made according to avariant of pump 1. The elements of pump 101 are designated by referencenumbers that are greater by 100 than the similar elements of pump 1.Only the modifications made in relation to pump 1 are describedhereafter.

Pump 101 comprises two identical pumping cells 101 a, 101 b, the part ofhousing 102 associated with cell 101 a consisting of a first element 102a comprising a cylindrical inlet that opens out and is connected along adiametral plane to part 102 b which progressively narrows and isconnected, along a diametral plane, to part 102 a of cell 101 b. The endpart 102 b of the latter delimits the outlet for the multiphaseeffluent. Part 102 b of the housing, provided with hydrodynamicdiffusers 112, forms the outer casing of homogenization chamber 111.

Hydraulic wheel 104 is here a semi-axial wheel and energy convertingdevice 105 comprises here two rotary helical wheels 110 a and 110 bwhich are axially shifted by a half-pitch, with an angular displacementof 180°.

The embodiments described above are of course not limitative and theycan be subjected to any desirable modification without departing fromthe scope of the invention.

What is claimed is:
 1. A cell for pumping a multiphase effluent,comprising: a fixed housing including an inlet and an outlet for themultiphase effluent, and a hydraulic wheel and an energy convertingdevice successively mounted on a common shaft axially arranged insidethe fixed housing; the hydraulic wheel including a first boss mounted onthe common shaft and carrying blades, the blades forming, between thefixed housing and the first boss, channels, and the energy convertingdevice including at least one helical wheel carried by a second bosswhich is mounted on the common shaft and which rotates in an energyhomogenization and transfer chamber delimited by the fixed housing, aratio of a section orthonormal to the axis of the energy homogenizationand transfer chamber to a sum of sections orthonormal to the axis of thechannels of the hydraulic wheel being 3 to
 10. 2. A pumping cellaccording claim 1, wherein the at least one helical wheel of the energyconverting device extends over an angle of at least 270°.
 3. A pumpingcell according to claim 1, wherein two helical wheels are provided forthe energy converting device, the two helical wheels being evenlyaxially shifted and exhibiting an angular displacement in relation toone another of 180°.
 4. A pumping cell according to claim 1, whereinthree helical wheels are provided for the energy converting device, thethree helical wheels being evenly axially shifted and exhibiting anangular displacement in relation to one another of 120°.
 5. A pumpingcell according to claim 1, wherein an angle of inclination of the atleast one helical wheel of the energy converting device in relation to aplane perpendicular to the common shaft in direction of the outlet ofthe fixed housing is of the order of 10°, and increases in the directionof the outlet up to 20°.
 6. A pumping cell according to claim 1, whereina ratio of an outside diameter Ds of said hydraulic wheel at the outletto the outside diameter De of the hydraulic wheel at the inlet isbetween 1 to
 3. 7. A pumping cell according to claim 1, wherein thechannels of the hydraulic wheel are identical, and between 4 and 10channels are provided.
 8. A pumping cell according to claim 6, wherein alength of the channels of the hydraulic wheel is${k \times \frac{{De} + {Ds}}{2}},$

where k ranges between 0.5 and 1.5.
 9. A pumping cell according to claim1, further comprising a flow diffuser device providing distribution andcontinuity of the flow at the outlet of hydraulic wheel over the totalsection of energy homogenization and transfer chamber of the associatedenergy converting device.
 10. A pumping cell according to claim 9,wherein the flow diffuser device comprises a grate with hydrodynamicprofiles, carried by the fixed housing and mounted in the energyhomogenization and transfer chamber between the inside of the fixedhousing and the at least one helical wheel.
 11. A method for using thepumping cell according to claim 1, comprising pumping an effluent withthe pumping cell, the effluent comprising a mixture of at least twophases selected from (a) a liquid phase including at least one liquid,(b) a gas phase including at least one free gas, and (c) a solid phaseincluding particles of at least one solid suspended in at least one ofthe liquid phase and the gas phase.
 12. A pump comprising at least onecell for pumping a multiphase effluent, the at least one cellcomprising: a fixed housing including an inlet and an outlet for themultiphase effluent, and a hydraulic wheel and an energy convertingdevice successively mounted on a common shaft axially arranged insidethe fixed housing; the hydraulic wheel including a first boss mounted onthe common shaft and carrying blades, the blades forming, between thefixed housing and the first boss, channels, and the energy convertingdevice including at least one helical wheel carried by a second bosswhich is mounted on the common shaft and which rotates in an energyhomogenization and transfer chamber delimited by the fixed housing, aratio of a section orthonormal to the axis of the energy homogenizationand transfer chamber to a sum of sections orthonormal to the axis of thechannels of the hydraulic wheel being 3 to
 10. 13. A pump according toclaim 12, comprising several of the cells mounted in series.